The underlying operating principles of a scroll type compressor are well-known in the art and many embodiments of such a compressor have been developed over the years. For example, a conventional scroll type compressor is shown in U.S. Pat. No. 801,182 issued to Creux. Such a compressor includes two scrolls each having a circular end plate and a spiroidal or involute spiral element. The scrolls are maintained angularly and radially offset so that both spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of the two scrolls shifts the line contacts along the spiral curved surfaces and, as a result, the volume of the fluid pockets changes. Since the volume of the fluid pockets increases or decreases dependent on the direction of the orbital motion, a scroll type fluid displacement apparatus may be used to compress, expand or pump fluids.
Another example of a conventional scroll type compressor which uses a bushing in the drive mechanism for the orbiting scroll is shown in published Japanese Patent Application No. 58-19,875. Such a compressor is similar in design to the one shown in FIG. 7 of the attached drawings.
In the compressor shown in FIG. 7, a fixed scroll 2 is fixedly disposed in compressor housing 1. Fixed scroll 2 is interfit with orbiting scroll 3 formed on an end surface of end plate 31. At least one fluid pocket is formed between fixed scroll 2 and orbiting scroll 3 as orbiting scroll 3 orbits about fixed scroll 2. A circular tubular boss 32 is formed on the other end surface of end plate 31. A diskshaped bushing 5 is rotatably disposed in boss 32 through needle bearing 6. A drive shaft 7 is rotatably supported within housing 1 through ball bearings 8 and 9. As shown in FIG. 8, eccentrically located hole 11 is formed through bushing 5 and receives crank pin 10. Crank pin 10 is attached to the inner end surface of drive shaft 7.
Thus, the rotation of drive shaft 7 is transmitted to orbiting scroll 3 through crank pin 10 and bushing 5.
Orbiting scroll 3 is prevented from rotating on its axis by a rotation preventing mechanism provided within the compressor. Therefore, as the orbiting scroll is moved while the fixed scroll remains stationary, the fluid pockets shift along the spiral curved surface of the scroll wraps, which changes the volume of the fluid pockets. However, due to the pressure of the compressor fluid, there is a tendency for the seal along the fluid pockets to become incomplete. Thus, a thrust bearing is provided for orbiting scroll 3 to help eliminate this problem.
In the above-mentioned conventional scroll apparatus, orbiting scroll 3 is supported by a thrust bearing comprising balls 12, an edge end portion of end plate 31 of orbiting scroll 3 and annular plate 31. Balls 12 serve as a rotation preventing mechanism for orbiting scroll 3 as shown in the above-mentioned publication of Japanese Patent Application No. 58-19,875.
When drive shaft 7 is rotated, orbiting scroll 3 orbits about fixed scroll 2 accordingly. Thus, fluid pockets 4 move toward the center of scrolls 2 and 3 which in turn decreases the volume of the fluid pockets, thereby compressing the fluid. The compressed fluid is forced to discharge chamber 14 through discharge hole 21 formed in end plate 22 of fixed scroll 2. The compressed fluid is discharged to the outside of housing 1 through a discharge port.
Disk-shaped bushing 5 shown in FIG. 7 is provided to insure that the fluid pockets formed by fixed scroll 2 and orbiting scroll 3 are securely sealed. Bushing 5 also eliminates any abnormal sealing of the fluid pockets due to manufacturing and assembly errors in the compressor.
As the fluid in fluid pockets 4 is compressed due to the operation of the compressor, orbiting scroll 3 is forced in both an axial and a radial direction. Since orbiting scroll 3 is supported against annular plate 13 by balls 12 at the edge end portion of end plate 31, the orbiting scroll is retrained from movement in the axial direction. Orbiting scroll 3 is not so retrained in the radial direction because the radial pressures acting on the orbiting scroll is not equal around the circumference of the scroll.
Accordingly, orbiting scroll 3 is urged in a direction which is determined by the crank angle 0' of crank pin 10. (See for example, FIG. 9.)
As can be seen in FIGS. 7 and 8, orbiting scroll 3 is operatively connected to drive shaft 7 by crank pin 7 through hole 11 formed in bushing 5. Orbiting scroll 3 is moved on needle bearing 6 mounted on boss 32. In conventional compressors, such as shown in FIG. 7, there is little or no clearance between the above elements. Thus, orbiting scroll 3 is prevented from radial movement due to the pressure of the compressed fluid in the fluid pockets. However, since drive shaft 7 is rotatably supported by ball bearings 8 and 9, drive shaft 7 can be radially moved within the distance of the radial clearance provided by bearings 8 and 9. Since the radial force, (shown by an arrow A in FIG. 9) which operates on orbiting scroll 3 also operates on the inner end of drive shaft 7 in the same direction as the radial motion of drive shaft 7, drive shaft 7 can be forced to rotate along axis 0'; for example, rather than along normal axis 0 as shown in FIG. 9. When this occurs, a gap may be created between bushing 5 and needle bearing 6 and between crank pin 10 and bushing 5. Such a situation results in the uneven engagement of bushing 5 with needle bearing 6. Accordingly, bushing 5 can be easily damaged during operation of the compressor.